Any cake mixture is loaded with carbs. It wouldn't be cake without the carbs. Sugar is pure carbohydrate. You should be looking for a low carb cake. The only way can keep a blood sugar down or keep a hypoglycemic from bottoming out is for the person to make sure they eat a meal with plenty of protein and fiber (as in vegies). That will help balance the carbs so it won't be as bad of a blood sugar spike. You can look for cakes with pureed fruit/carrots, etc to add fiber and sweetness. I'm sure there are plenty of cc'ers that can help with that.

For a frosting, there's a CC recipe called Sugar-Free Whipped Cream Frosting. You just whisk together 1 cup milk and 1 small box sugar-free instant pudding of any flavor. Then, with an electric mixer, beat in1 pint heavy cream until stiff peaks form. It makes about 4 cups.